Dementia is a category of brain disease which is characterized by a long term, often gradual, decrease in a person's memory or other thinking skills that is great enough to affect daily functioning. Common causes of dementia include Alzheimer's disease, vascular dementia, Lewy body dementia, and frontotemporal dementia. A person may suffer from more than one type of dementia.
While symptoms can vary greatly, diagnosis of dementia can be made when one or more of the following core mental functions are significantly impaired; memory, communication and language, ability to focus and pay attention, reasoning and judgment, and visual perception. Health care costs for dementia have been found to be greater than that of any other disease. According to the National Institutes of Health, total spending for people with dementia in the last five years of life was more than a quarter-million dollars per person.
The types of memory systems that may be affected by dementia include episodic memory, semantic memory, simple classical conditioning, procedural memory, working memory, and priming (Gold, C. A. and Budson, A. E. “Memory loss in Alzheimer's disease: implications for development of therapeutics,” Expert Rev. Neurother. 8(12):1879-91 (2008)). Each of these types of memory systems may be differentially affected depending on disease. Episodic memory facilitates individuals to remember events, times and places acquired through personal experience. Impairment of episodic memory is often one of the earliest signs and symptoms of dementia and directly linked to pathologic lesions within the hippocampus, a critical region of the brain for episodic memory formation. Of the memory systems most authors consider the episodic memory system to be the most clinically relevant for dementia, as impairments in this system can worsen memory for recent events, leading to functional deficits (Tromp D, Duour A, Lithfous S, Pebayle T, Despres O. “Episodic memory in normal ageing and Alzheimer disease: Insights from imaging and behavioral studies.” Ageing Res Rev. (2015); 24:232-62).
Episodic memory can be assessed by clinical tests such the Wechsler Memory Scale (WMS) or Hopkins Verbal Learning Test—Revised (HVLT-R). In clinical practice, episodic memory may also be assessed by components of the Mini-Mental State Examination (MMSE).
The WMS is a neuropsychological test designed to measure different memory functions in a human subject. The current version of this test, the WMS-IV is made up of seven subtests: Spatial Addition, Symbol Span, Design Memory, General Cognitive Screener, Logical Memory(I & II), Verbal Paired Associates(I & II), and Visual Reproduction(I & II). A person's performance is reported as five Index Scores: Auditory Memory, Visual Memory, Visual Working Memory, Immediate Memory, and Delayed Memory. The latter two Index scores (i.e Immediate and Delayed Memory, respectively) specifically assess episodic memory.
The HVLT-R is a measure of verbal episodic memory that consists of 3 initial learning trials, a delayed recall trial and a yes/no delayed recognition trial. The HVLT-R comes in 6 alternative and parallel forms, thereby reducing the potential of a practice effect.
The MMSE is a brief evaluation of orientation, registration, attention, recall, language, and constructional praxis. The MMSE is highly reproducible and is a useful tool for evaluating the mental state and abilities of human patients. In addition to its value in screening patients for dementia or patients at risk for dementia, the MMSE is often used to document cognitive decline over time in individual patients. (Clark, C. M. et al., “Variability in annual Mini-Mental State Examination score in patients with probable Alzheimer disease; a clinical perspective of data from the Consortium to Establish a Registry for Alzheimer's Disease,” Arch Neurol. July; 56(7):857-62 (4999)).